Light-reflective conductive particle, anisotropic conductive adhesive and light-emitting device

ABSTRACT

A light-reflective conductive particle for an anisotropic conductive adhesive used for anisotropic conductive connection of a light-emitting element to a wiring board includes a core particle coated with a metal material and a light-reflecting layer formed from light-reflective inorganic particles having a refractive index of 1.52 or more on a surface of the core particle. Examples of the light-reflective inorganic particles having a refractive index of 1.52 or more include titanium oxide particles, zinc oxide particles, or aluminum oxide particles.

TECHNICAL FIELD

The present invention relates to a light-reflective conductive particlefor an anisotropic conductive adhesive used for anisotropic conductiveconnection of a light-emitting element to a wiring board, an anisotropicconductive adhesive containing the same, and a light-emitting deviceformed by using this adhesive to mount a light-emitting element to awiring board.

BACKGROUND ART

Light-emitting devices that use a light-emitting diode (LED) element arewidely used. Older-type light-emitting devices are configured by, asillustrated in FIG. 4, joining an LED element 33 to a substrate 31 witha die bond adhesive 32, wire-bonding a p electrode 34 and an n electrode35 on an upper face of the LED element 33 to a connection terminal 36 onthe substrate 31 with a gold wire 37, and then sealing the whole of theLED element 33 with a transparent mold resin 38. However, for thelight-emitting device illustrated in FIG. 4, there is the problem that,among the light emitted by the LED element 33, the light having awavelength of 400 to 500 nm that is output to the upper face side isabsorbed by the gold wire, and a part of the light output to the lowerface side is absorbed by the die bond adhesive 32, whereby thelight-emitting efficiency of the LED element 33 deteriorates.

Consequently, as illustrated in FIG. 5, flip chip mounting of the LEDelement 33 has been proposed (Patent Literature 1). In this flip chipmounting technique, a bump 39 is formed on both the p electrode 34 andthe n electrode 35. Furthermore, a light-reflecting layer 40 is providedon the surface of the LED element 33 on which the bumps are formed sothat the p electrode 34 and the n electrode 35 are insulated. The LEDelement 33 and the substrate 31 are fixedly connected using ananisotropic conductive paste 41 or an anisotropic conductive film (notillustrated), and curing the paste or film. Consequently, in thelight-emitting device illustrated in FIG. 5, the light output toward theupper side of the LED element 33 is not absorbed by the gold wire, andmost of the light output toward the lower side is reflected by thelight-reflecting layer 40 and is output upwards. As a result, thelight-emitting efficiency (light extraction efficiency) does notdeteriorate.

CITATION LIST Patent Literature

-   [Patent Document 1] Japanese Patent Application Laid-Open No. Hei.    11-168235

SUMMARY OF INVENTION Problems to be Solved by the Invention

However, with the technique described in Patent Document 1, thelight-reflecting layer 40 has to be provided on the LED element 33 by amethod such as metal vapor deposition so that the p electrode 34 and then electrode 35 are insulated. Therefore, from a production perspective,there is the problem that an increase in costs cannot be avoided.

On the other hand, if the light-reflecting layer 40 is not provided, thesurface of the conductive particles coated with gold, nickel, or copperin the cured anisotropic conductive paste or anisotropic conductive filmexhibit a color that is from brown to dark brown. Further, the epoxyresin binder in which the conductive particles are dispersed itself alsoexhibits a brown color due to the imidazole latent curing agent that isnormally used for curing. Consequently, there are the problems that itis difficult to improve the light-emitting efficiency (light extractionefficiency) of the light emitted by the light-emitting element, and thatthe color of the emitted light (emission color) could not be reflectedas that color without change.

It is an object of the present invention to resolve the above-describedproblems in the conventional art, and to provide a light-reflectiveconductive particle that does not reduce light-emitting efficiency anddoes not produce a hue difference between the emission color of thelight-emitting element and the reflected color even if alight-reflecting layer that causes production costs to increase is notprovided on a light-emitting diode (LED) element, when producing alight-emitting device by flip-chip mounting a light-emitting elementsuch as an LED element on a wiring board using an anisotropic conductiveadhesive. Further, it is an object of the present invention is toprovide an anisotropic conductive adhesive containing thelight-reflective conductive particle, as well as a light-emitting deviceformed by using this adhesive to mount a light-emitting element to awiring board.

Means for Solving the Problems

Based on the hypothesis that deterioration in light-emitting efficiencycan be prevented if an anisotropic conductive adhesive itself is made tohave a light-reflecting function, the present inventor has found thatdeterioration in the light-emitting efficiency of a light-emittingelement and the occurrence of a hue difference between the emissioncolor of the light-emitting element and the color reflected from theconductive particles can be prevented by providing a light-reflectinglayer having a white to grey color formed from specific inorganicparticles on the surface of conductive particles that are blended in ananisotropic conductive adhesive, thereby completing the presentinvention.

Specifically, the present invention provides a light-reflectiveconductive particle for an anisotropic conductive adhesive used foranisotropic conductive connection of a light-emitting element to awiring board, comprising a core particle coated with a metal materialand a light-reflecting layer formed from light-reflective inorganicparticles having a refractive index of 1.52 or more on a surface of thecore particle.

Further, the present invention provides an anisotropic conductiveadhesive used for anisotropic conductive connection of a light-emittingelement to a wiring board, the adhesive comprising the above-describedlight-reflective conductive particle dispersed in a thermosetting resincomposition that forms a cured product having a light transmittance (JISK7105) of 80% or more at a light path length of 1 cm to visible lighthaving a wavelength of 380 to 780 nm.

In addition, the present invention provides a light-emitting deviceformed by mounting a light-emitting element by a flip-chip mountingmethod to a wiring board with the above-described light-reflectiveanisotropic conductive adhesive provided therebetween.

Advantageous Effects of the Invention

The light-reflective conductive particle of the present invention for ananisotropic conductive adhesive used for anisotropic conductiveconnection of a light-emitting element to a wiring board is formed froma core particle coated with a metal material and a light-reflectinglayer which has a white to grey color and is formed fromlight-reflective inorganic particles having a refractive index of 1.52or more on a surface of the core particle. Further, the anisotropicconductive adhesive of the present invention comprises thislight-reflective conductive particle dispersed in a thermosetting resincomposition that forms a cured product having a light transmittance (JISK7105) of 80% or more at a light path length of 1 cm to visible lighthaving a wavelength of 380 to 780 nm. Therefore, a light-emitting deviceobtained using the anisotropic conductive adhesive of the presentinvention does not discolor even if the anisotropic conductive adhesiveis cured. Moreover, since the included light-reflective conductiveparticles have a low dependence of the reflecting property to thewavelength of the visible light, light-emitting efficiency can beimproved, and the emission color of the light-emitting element can bereflected as that color without change.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-sectional view of a light-reflective conductiveparticle of the present invention for an anisotropic conductiveadhesive.

FIG. 1B is a cross-sectional view of a light-reflective conductiveparticle of the present invention for an anisotropic conductiveadhesive.

FIG. 2 is a cross-sectional view of a light-emitting device of thepresent invention.

FIG. 3 is a graph illustrating the light reflectance of the curedproducts of the anisotropic conductive adhesives of Example 1 andComparative Example 1 with respect to wavelength.

FIG. 4 is a cross-sectional view of a conventional light-emittingdevice.

FIG. 5 is a cross-sectional view of a conventional light-emittingdevice.

DESCRIPTION OF EMBODIMENTS

The present invention will now be described in more detail withreference to the drawings.

FIGS. 1A and 1B are cross-sectional views of light-reflective conductiveparticles 10 and 20 of the present invention for an anisotropicconductive adhesive. First, the light-reflective conductive particles ofFIG. 1A will be described.

The light-reflective conductive particle 10 is formed from a coreparticle 1 coated with a metal material and a light-reflecting layer 3formed from light-reflective inorganic particles 2 having a refractiveindex of 1.52 or more that are on the surface of the core particle 1.

The light-reflective inorganic particles 2 having a refractive index of1.52 or more are inorganic particles that look white under sunlight.Therefore, the light-reflecting layer 3 formed from these particlesexhibits a color from white to grey. The fact that this layer exhibits acolor from white to grey means that the dependence of the reflectingproperty to the wavelength of the visible light is small, and thatvisible light is easily reflected.

Examples of the preferred light-reflective inorganic particles 2 includeat least one kind selected from titanium oxide (TiO₂) particles, zincoxide (ZnO) particles, and aluminum oxide (Al₂O₃) particles. Among thetitanium oxide particles, zinc oxide particles, or aluminum oxideparticles, if there are concerns about light degradation of the curedproduct of the thermosetting resin in the cured anisotropic conductiveadhesive, zinc oxide, which does not exhibit a catalytic activity tolight degradation and has the highest refractive index, can bepreferably used.

Since the core particle 1 is used for anisotropic conductive connection,the surface of the core particle 1 is formed from a metal material.Modes in which the surface is coated with a metal material include amode in which the core particle 1 itself is a metal material, and a modein which the surface of a resin particle is coated with a metalmaterial.

As the metal material, metal materials that are conventionally used asconductive particles for anisotropic conductive connection can be used.Examples thereof include gold, nickel, copper, silver, solder,palladium, aluminum, alloys thereof, multilayer composites thereof(e.g., a nickel plating/gold flash plating composite) and the like.Among these, gold, nickel, and copper can exhibit the advantages effectsof the present invention more than other metal materials, as they makethe conductive particles brown.

If the core particle 1 is formed by coating a metal material on a resinparticle, the resin particle portion of a conventionally-usedmetal-coated resin particle can be employed as the conductive particlefor anisotropic conductive connection. Examples of such resin particlesinclude styrene resin particles, benzoguanamine resin particles, nylonresin particles and the like. A conventionally-known method may beemployed for coating the resin particles with a metal material. Forexample, an electroless plating method or an electroplating method maybe utilized. Further, the thickness of the coated metal material is athickness that is sufficient to ensure a good connection reliability.Although this depends on the particle size of the resin particles andthe type of metal, usually, the thickness is 0.1 to 3 μm, and preferably0.1 to 1 μm.

Further, if the particle size of the core particle 1 having a metalmaterial surface is too small, electrical continuity failures tend tooccur, while if the particle size is too large, short circuits betweenpatterns tend to occur. Therefore, the particle size is preferably 1 to20 μm, more preferably 3 to 5 μm, and especially preferably 3 to 5 μm.In this case, it is preferred that the shape of the core particle 1 bespherical, although the shape may also be flake-like or a rugby ballshape.

When viewed from the perspective of relative size to the particle sizeof the core particle 1, if the thickness of the light-reflecting layer 3formed from the light-reflective inorganic particles 2 is too small withrespect to the core particle 1 particle size, reflectance tends todeteriorates, while if this thickness is too large, electricalcontinuity failures tend to occur. Therefore, the thickness ispreferably 0.5 to 50%, and more preferably 1 to 25% of the particle sizeof the core particle 1.

Further, in the light-reflective conductive particle 10, if the particlesize of the light-reflective inorganic particles 2 forming thelight-reflecting layer 3 is too small, it tends to be difficult toproduce a light-reflecting phenomenon, while if this particle size istoo large, it tends to be difficult to form the light-reflecting layer.Therefore, the particle size is preferably 0.02 to 4 μm, more preferably0.1 to 1 μm, and especially preferably 0.2 to 0.5 μm. In this case, fromthe perspective of the wavelength of the light that is reflected, it ispreferred that the particle size of the light-reflective inorganicparticles 2 be 50% or more of the wavelength of that light so that thelight that should be reflected (i.e., the light emitted by thelight-emitting element) does not pass through. In this case, examples ofthe shape of the light-reflective inorganic particles 2 includeamorphous, spherical, scale-like, needle-like and the like. However,among these, from the perspective of a light diffusion effect, sphericalis preferred, and from a total reflection effect, a scale-like shape ispreferred.

The light-reflective conductive particle 10 illustrated in FIG. 1A canbe produced by a known deposition technology (so-called mechanofusion)in which a film formed from small particles on the surface of largeparticles is formed by making the small and large powders physicallycollide. In this case, the light-reflective inorganic particles 2 arefixed so as to bite the metal material on the surface of the coreparticles 1. On the other hand, it is difficult to make inorganicparticles fuse and fix together. Accordingly, a monolayer of inorganicparticles forms the light-reflecting layer 3. Therefore, in the case ofFIG. 1A, the thickness of the light-reflecting layer 3 can be consideredto be the same to slightly thinner than the particle size of thelight-reflective inorganic particles 2.

Next, the light-reflective conductive particle 20 illustrated in FIG. 1Bwill be described. The light-reflective conductive particle 20 differsfrom the light-reflective conductive particle 10 of FIG. 1A in includinga thermoplastic resin 4 in which the light-reflecting layer 3 functionsas an adhesive, and in that the light-reflective inorganic particles 2themselves are also fixed by this thermoplastic resin 4 so that thelight-reflective inorganic particles 2 form a multilayer structure (forexample, a two- or three-layer multilayer structure). By including sucha thermoplastic resin 4, the mechanical strength of the light-reflectinglayer 3 improves, and it is more difficult for the inorganic particlesto fall off and the like.

The light-reflective conductive particle 20 illustrated in FIG. 1B canalso be produced by mechanofusion. In this case, in addition to thelight-reflective inorganic particles 2 and the core particle 1, aparticulate thermoplastic resin 4 can also be used. When producing thelight-reflective conductive particle 20 illustrated in FIG. 1B bymechanofusion, the light-reflective conductive particle 10 illustratedin FIG. 1A is also produced at the same time.

In consideration of reducing the burden on the environment, it ispreferred to use a halogen-free thermoplastic resin as the thermoplasticresin 4. For example, it is preferred to use a polyolefin such aspolyethylene and polypropylene, a polystyrene, an acrylic resin and thelike.

Such a light-reflective conductive particle 20 can also be produced bymechanofusion. If the particle size of the thermoplastic resin 4employed in mechanofusion is too small, its effect as an adhesive isreduced, while if this particle size is too large, it is more difficultfor the resin to adhere to the core particle 1. Therefore, the particlesize is preferably 0.02 to 4 μm, and more preferably 0.1 to 1 μm.Further, if the blended amount of such a thermoplastic resin 4 is toolow, its effect as an adhesive is reduced, while if this blended amountis too much, unintended particle agglomerates form. Therefore, theblended amount is preferably, based on 100 parts by mass of the coreparticle 1, 0.2 to 500 parts by mass, and more preferably 4 to 25 partsby mass.

Next, the anisotropic conductive adhesive of the present invention willbe described. This anisotropic conductive adhesive includes thelight-reflective conductive particle of the present invention dispersedin a thermosetting resin composition, and may be in the form of a paste,film or the like.

It is preferred to use a composition that is as colorless andtransparent as possible for the thermosetting resin composition used inthe anisotropic conductive adhesive of the present invention. This is toprevent deterioration in the light reflection efficiency of thelight-reflective conductive particles in the anisotropic conductiveadhesive, and to reflect the incident light without changing its color.Here, “colorless and transparent” means a light transmittance (JISK7105) of 80% or more, and preferably 90% or more, at a light pathlength of 1 cm to visible light having a wavelength of 380 to 780 nm.

In the anisotropic conductive adhesive of the present invention, if theblended amount of the light-reflective conductive particles based on 100parts by mass of the thermosetting resin composition is too low,electrical continuity failures tend to occur, while if the blendedamount is too much, short circuits between patterns tend to occur.Therefore, the blended amount is preferably 1 to 100 parts by mass, andmore preferably 10 to 50 parts by mass.

Concerning the reflection properties of the anisotropic conductiveadhesive of the present invention, to improve the light-emittingefficiency of the light-emitting element, it is preferred that thereflectance (JIS K7105) of a 100 μm-thick cured product of theanisotropic conductive adhesive to light with a wavelength of 450 nm beat least 15%. To obtain such a reflectance, the reflection propertiesand blended amount of the used light-reflective conductive particles,and the blended composition of the thermosetting resin composition maybe appropriately adjusted. Generally, if the blended amount oflight-reflective conductive particles having good reflection propertiesis increased, the reflectance also tends to increase.

The reflection properties of the anisotropic conductive adhesive canalso be evaluated from the perspective of refractive index (JIS K7142).Specifically, this is because if the difference in the refractive indexof the thermosetting resin composition of the anisotropic conductiveadhesive and that of the light-reflective conductive particles is toolarge, the light reflection amount at the interface between thelight-reflective conductive particles and the cured product of thethermosetting resin composition encircling those particles increases.More specifically, it is preferred that the difference in the refractiveindex between the thermosetting resin composition and thelight-reflective inorganic particles be 0.02 or more, and preferably 0.3or more. Generally, the refractive index of the thermosetting resincomposition that mainly contains the epoxy resin is approximately 1.5.

As the thermosetting resin composition constituting the anisotropicconductive adhesive of the present invention, a resin composition thatis used in conventional anisotropic conductive adhesives and anisotropicconductive films can be used. Generally, such a thermosetting resincomposition blends a curing agent in an insulating binder resin.Preferred examples of the insulating binder resin include epoxy resinshaving an alicyclic epoxy resin, a heterocyclic epoxy resin, ahydrogenated epoxy resin or the like as a main component.

It is preferred that the alicyclic epoxy compound have two or more epoxygroups in the molecule. The alicyclic epoxy compound may be a liquid ora solid. Specific examples include glycidyl hexahydrobisphenol A,3,4-epoxycyclohexenylmethyl-3′,4′-epoxycyclohexene carboxylate and thelike. Among these, from the perspectives of ensuring that the curedproduct has an optical transparency suitable for mounting an LED elementand the like, and excellent fast-curing properties, it is preferred touse glycidyl hexahydrobisphenol. A or3,4-epoxycyclohexenylmethyl-3′,4′-epoxycyclohexene carboxylate.

Examples of heterocyclic epoxy compounds include epoxy compounds havinga triazine ring. Especially preferred is1,3,5-tris(2,3-epoxypropyl)-1,3,5-triazine-2,4,6-(1H,3H,5H)-trione.

As the hydrogenated epoxy compound, hydrogenated products of theabove-described alicyclic epoxy compounds and heterocyclic epoxycompounds, and other well-known hydrogenated epoxy resins can be used.

The alicyclic epoxy compound, heterocyclic epoxy compound, andhydrogenated epoxy compound may be used alone, or two or more kinds maybe used together. In addition to these epoxy compounds, other epoxycompounds can also be used, as long as the effects of the presentinvention are not harmed. Examples thereof include known epoxy resinssuch as: glycidyl ethers obtained by reacting epichlorohydrin with apolyhydric phenol such as bisphenol A, bisphenol F, bisphenol S,tetramethylbisphenol A, diallylbisphenol A, hydroquinone, catechol,resorcin, cresol, tetrabromobisphenol A, trihydroxybiphenyl,benzophenone, bisresorcinol, bisphenol hexafluoroacetone,tetramethylbisphenol A, tetramethylbisphenol F,tris(hydroxyphenyl)methane, bixylenol, phenol-novolac, orcresol-novolac; polyglycidyl ethers obtained by reacting epichlorohydrinwith an aliphatic polyhydric alcohol such as glycerin, neopentyl glycol,ethylene glycol, propylene glycol, butylene glycol, hexylene glycol,polyethylene glycol, or polypropylene glycol; glycidyl ether estersobtained by reacting epichlorohydrin with a hydroxycarboxylic acid suchas p-oxybenzoic acid or β-oxynaphthoic acid; polyglycidyl estersobtained from polycarboxylic acids such as phthalic acid, methylphthalicacid, isophthalic acid, terephthalic acid, tetrahydrophthalic acid,endomethylene tetrahydrophthalic acid, endomethylene hexahydrophthalicacid, trimellitic acid, and polymerized fatty acids;glycidylaminoglycidyl ethers obtained from aminophenols andaminoalkylphenols; glycidylaminoglycidyl esters obtained fromaminobenzoic acids; glycidylamines obtained from aniline, toluidine,tribromoaniline, xylylenediamine, diamino cyclohexane,bisaminomethylcyclohexane, 4,4′-diaminodiphenyl methane, and4,4′-diaminodiphenyl sulfone; and epoxydized polyolefins.

Examples of curing agents that can be used include acid anhydrides,imidazole compounds, cyanogens and the like. Among these, it ispreferred to use acid anhydrides that tend not to change the color ofthe cured product, especially an alicyclic acid anhydride curing agent.A specific preferred example that can be used is methylhexahydrophthalic anhydride (MeHHPA).

When using an alicyclic epoxy compound and an alicyclic acid anhydridecuring agent in the thermosetting resin composition of the anisotropicconductive adhesive of the present invention, if the used amount of thealicyclic acid anhydride curing agent is too low, the curing defectstend to occur due to an increased amount of uncured epoxy compound,while if the used amount is too much, corrosion of the coated materialtends to be promoted due to the influence of excess curing agent.Therefore, it is preferred to use the alicyclic acid anhydride curingagent in a ratio of, based on 100 parts by mass of alicyclic epoxycompound, 80 to 120 parts by mass, and more preferably 95 to 105 partsby mass.

The anisotropic conductive adhesive of the present invention can beproduced by uniformly mixing the light-reflective conductive particlesand the thermosetting resin composition. Further, if using theanisotropic conductive adhesive as an anisotropic conductive film, thisfilm can be obtained by dispersing and mixing the above materials in asolvent such as toluene, coating the resultant mixture to a desiredthickness on a release-treated PET film, and then drying at atemperature of about 80° C.

Next, the light-emitting device of the present invention will bedescribed with reference to FIG. 2. A light-emitting device 200 is alight-emitting device in which a substrate 21 and an LED element 23 areflip-chip mounted, formed by coating the above-described anisotropicconductive adhesive of the present invention between a connectionterminal 22 on the substrate 21 and connection bumps 26 respectivelyformed on an n electrode 24 and a p electrode 25 of the LED element 23as a light-emitting element. Here, the cured product 100 of theanisotropic conductive adhesive is formed with light-reflectiveconductive particles 10 dispersed in a cured product 11 of thethermosetting resin composition. Optionally, a transparent mold resinmay be applied so as to seal the whole of the LED element 23.

In the thus-configured light-emitting device 200, of the light emittedby the LED element 23, the light emitted toward the substrate 21 side isreflected by the light-reflective conductive particles 10 in the curedproduct 100 of the anisotropic conductive adhesive, and is output fromthe upper face of the LED element 23. Therefore, a deterioration in thelight-emitting efficiency can be prevented.

EXAMPLES Example 1 Production of Light-Reflective Conductive Particles

The light-reflective conductive particles of Example 1 were obtained byadding 4 parts by mass of a titanium oxide powder having an averageparticle size of 0.5 μm (KR-380, Titan Kogyo, Ltd.) and 20 parts by massof Au-coated resin conductive particles having a brown appearance and anaverage particle size of 5 μm (particles formed by coating a 0.2μm-thick electroless gold plating on spherical acrylic resin particleshaving an average particle size of 4.6 μm (Bright 20GNB4.6 EH, NipponChemical Industrial Co., Ltd.)) to a mechanofusion apparatus (AMS-GMP,Hosokawa Micron Corporation), and depositing an approximately 0.3μm-thick light-reflecting layer formed from the titanium oxide particleson the surface of the conductive particles under conditions of arotation speed of 1,000 rpm and a rotation time of 20 minutes. Theappearance of these light-reflective conductive particles was grey.

(Light Reflectance Evaluation Test)

15 parts by mass of the obtained light-reflective conductive particlesand 100 parts by mass of a colorless, transparent thermosetting epoxybinder composition having a refractive index of approximately 1.5(YX-8000, Mitsubishi Chemical Corporation) were uniformly mixed using avacuum defoaming stirring apparatus to obtain the anisotropic conductiveadhesive of Example 1.

The obtained anisotropic conductive adhesive was coated on a whiteceramic plate to a dry thickness of 100 μm, and heated for 1 minute at200° C. to cure. The reflectance of this cured product to light with awavelength of 450 nm (JIS K7105) was measured using a spectrophotometer(U3300, Hitachi, Ltd.). The obtained results are shown in Table 1 and inFIG. 3.

(Electrical Properties (Continuity Reliability, Insulation Reliability)Evaluation Test)

Using the anisotropic conductive adhesive prepared during the lightreflectance evaluation test, a 6 mm-square test IC chip (conductorconnection surface area/conductor−space=1,600 μm²/50 μmP) having 15μm-high gold bumps was flip-chip mounted on a glass epoxy substratehaving wires formed by plating Ni/Au (5.0 μm thick/0.3 μm thick) on acopper wire at a 50 μm pitch under conditions of 200° C., 60 seconds,and 1 Kg/chip to obtain a test IC module.

1. Continuity Reliability

The obtained test IC module was subjected to a temperature cycle test(TCT) (JIS C5030) of alternately heating and cooling to a hottemperature (100° C.) and a cold temperature (−40° C.), and the initialresistance and the resistance after 500 cycles were measured by afour-terminal method. Cases in which resistance was less than 1Ω wereevaluated with rank A, and cases in which resistance was 1Ω or more wereevaluated with rank C. The obtained results are shown in Table 1.

2. Insulation Reliability

A separately-produced test IC module was subjected to an aging test ofleaving for 1,000 hours under an 85° C., 85% RH environment, and theinitial resistance and the resistance after 1,000 hours were measured.Cases in which resistance was 10⁶Ω or more were evaluated with rank A,and cases in which resistance was less than 10⁶Ω were evaluated withrank C. The obtained results are shown in Table 1.

Example 2

Light-reflective conductive particles having a grey appearance, and ananisotropic conductive adhesive, were obtained in the same manner as inExample 1, except that Ni-coated resin conductive particles having anaverage particle size of 5.0 μm (52NR-4.6 EH, Nippon Chemical IndustrialCo., Ltd.) were used instead of Au-coated resin conductive particles.Further, a light reflectance evaluation test and an electricalproperties (continuity reliability, insulation reliability) evaluationtest were also carried out in the same manner as in Example 1. Theobtained results are shown in Table 1.

Example 3

Light-reflective conductive particles having a grey appearance wereobtained by adding 4 parts by mass of a titanium oxide powder having anaverage particle size of 0.5 μm (KR-380, Titan Kogyo, Ltd.), 3 parts bymass of polystyrene (PS) particles having an average particle size of0.2 μm (Glossdell 204S, Mitsui Chemicals, Inc.) as adhesive particles,and 20 parts by mass of conductive particles having an average particlesize of 5 μm (particles formed by coating a 0.2 μm-thick electrolessgold plating on spherical acrylic resin particles having an averageparticle size of 4.6 μm (Bright 20GNB4.6 EH, Nippon Chemical IndustrialCo., Ltd.) to a mechanofusion apparatus (AMS-GMP, Hosokawa MicronGroup), and depositing an approximately 1 μm-thick light-reflectinglayer formed from styrene and titanium oxide particles on the surface ofthe conductive particles under conditions of a rotation speed of 1,000rpm and a rotation time of 20 minutes. Then, an anisotropic conductiveadhesive was obtained. Further, a light reflectance evaluation test andan electrical properties (continuity reliability, insulationreliability) evaluation test were also carried out in the same manner asin Example 1. The obtained results are shown in Table 1.

Example 4

Light-reflective conductive particles having a grey appearance, and ananisotropic conductive adhesive, were obtained in the same manner as inExample 3, except that Ni-coated resin conductive particles having anaverage particle size of 5.0 μm (52NR-4.6 EH, Nippon ChemicalIndustrial. Co., Ltd.) were used instead of Au-coated resin conductiveparticles. Further, a light reflectance evaluation test and anelectrical properties (continuity reliability, insulation reliability)evaluation test were also carried out in the same manner as inExample 1. The obtained results are shown in Table 1.

Example 5

Light-reflective conductive particles having a grey appearance, and ananisotropic conductive adhesive, were obtained in the same manner as inExample 3, except that polyethylene (PE) particles having an averageparticle size of 0.2 μm (Amiparl WF300, Mitsui Chemicals, Inc.) wereused instead of the polystyrene particles having an average particlesize of 0.2 μm (Glossdell 204S, Mitsui Chemicals, Inc.). Further, alight reflectance evaluation test and an electrical properties(continuity reliability, insulation reliability) evaluation test werealso carried out in the same manner as in Example 1. The obtainedresults are shown in Table 1.

Example 6

Light-reflective conductive particles having a grey appearance, and ananisotropic conductive adhesive, were obtained in the same manner as inExample 3, except that a zinc oxide powder having an average particlesize of 0.5 μm (one kind of zinc oxide, Hakusuitech, Ltd.) was usedinstead of the titanium oxide powder having an average particle size of0.5 μm. Further, a light reflectance evaluation test and an electricalproperties (continuity reliability, insulation reliability) evaluationtest were also carried out in the same manner as in Example 1. Theobtained results are shown in Table 1.

Example 7

Light-reflective conductive particles having a grey appearance, and ananisotropic conductive adhesive, were obtained in the same manner as inExample 3, except that an aluminum oxide powder having an averageparticle size of 0.5 μm (AE-2500S1, Admatechs, Co., Ltd.) was usedinstead of the titanium oxide powder having an average particle size of0.5 μm. Further, a light reflectance evaluation test and an electricalproperties (continuity reliability, insulation reliability) evaluationtest were also carried out in the same manner as in Example 1. Theobtained results are shown in Table 1.

Example 8

Light-reflective conductive particles having a grey appearance, and ananisotropic conductive adhesive, were obtained in the same manner as inExample 3, except that magnesium carbonate having an average particlesize of 0.5 μm was used instead of the titanium oxide powder having anaverage particle size of 0.5 μm. Further, a light reflectance evaluationtest and an electrical properties (continuity reliability, insulationreliability) evaluation test were also carried out in the same manner asin Example 1. The obtained results are shown in Table 1.

Example 9

Light-reflective conductive particles having a grey appearance, and ananisotropic conductive adhesive, were obtained in the same manner as inExample 3, except that a titanium oxide powder having an averageparticle size of 0.2 μm (JR405, Tayca Corporation) was used instead ofthe titanium oxide powder having an average particle size of 0.5 μm.Further, a light reflectance evaluation test and an electricalproperties (continuity reliability, insulation reliability) evaluationtest were also carried out in the same manner as in Example 1. Theobtained results are shown in Table 1.

Comparative Example 1

An anisotropic conductive adhesive was obtained in the same manner as inExample 1 using Au-coated resin conductive particles having a brownappearance (particles formed by coating a 0.2 μm-thick electroless goldplating on spherical acrylic resin particles having an average particlesize of 4.6 μm (Bright 20GNB4.6 EH, Nippon Chemical Industrial Co.,Ltd.). Further, a light reflectance evaluation test and an electricalproperties (continuity reliability, insulation reliability) evaluationtest were also carried out in the same manner as in Example 1. Theobtained results are shown in Table 1. The light reflectance is alsoillustrated in FIG. 3.

Comparative Example 2

An anisotropic conductive adhesive was obtained in the same manner as inComparative Example 1, except that Ni-coated resin conductive particleshaving a brown appearance and an average particle size of 5.0 μm(52NR-4.6 EH, Nippon Chemical Industrial Co., Ltd.) were used instead ofAu-coated resin conductive particles. Further, a light reflectanceevaluation test and an electrical properties (continuity reliability,insulation reliability) evaluation test were also carried out in thesame manner as in Example 1. The obtained results are shown in Table 1.

Comparative Example 3

Light-reflective conductive particles having a brown appearance wereobtained by adding 3 parts by mass of polystyrene particles having anaverage particle size of 0.2 μm (Glossdell 204S, Mitsui Chemicals, Inc.)and 20 parts by mass of conductive particles having an average particlesize of 5 μm (particles formed by coating a 0.2 μm-thick electrolessgold plating on spherical acrylic resin particles having an averageparticle size of 4.6 μm (Bright 20GNB4.6 EH, Nippon Chemical IndustrialCo., Ltd.)) to a mechanofusion apparatus (AMS-GMP, Hosokawa MicronGroup), and depositing a 0.2 μm-thick styrene layer on the surface ofthe conductive particles under conditions of a rotation speed of 1,000rpm and a rotation time of 20 minutes. Then, an anisotropic conductiveadhesive was obtained. Further, a light reflectance evaluation test andan electrical properties (continuity reliability, insulationreliability) evaluation test were also carried out in the same manner asin Example 1. The obtained results are shown in Table 1.

Comparative Example 4

Conductive particles having a brown appearance, and an anisotropicconductive adhesive, were obtained in the same manner as in Example 3,except that a silicon oxide powder having an average particle size of0.5 μm (Seahosta KEP-30, Nippon Shokubai Co., Ltd.) was used instead ofthe titanium dioxide powder having an average particle size of 0.5 μm.Further, a light reflectance evaluation test and an electricalproperties (continuity reliability, insulation reliability) evaluationtest were also carried out in the same manner as in Example 1. Theobtained results are shown in Table 1.

TABLE 1 EXAMPLE COMPARATIVE EXAMPLE 1 2 3 4 5 6 7 8 9 1 2 3 4 RawMaterial Surface Metal Au Ni Au Ni Au Au Au Au Au Au Ni Au Au ConductiveParticle Size 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0Particles (μm) Adhesive Type — — PS PS PE PS PS PS PS — — PS PSParticles Particle Size — — 0.2 0.2 0.1 0.2 0.2 0.2 0.2 — — 0.2 0.2 (μm)Inorganic Type TiO₂ TiO₂ TiO₂ TiO₂ TiO₂ ZnO Al₂O₃ MgCO₃ TiO₂ — — — SiO₂Particles Particle Size 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.2 — — — 0.5(μm) Refractive  2.71  2.71  2.71  2.71  2.71  1.95  1.76  1.52  2.71 —— —  1.45 Index n1 Light- Color Grey Grey Grey Grey Grey Grey Grey GreyGrey Brown Black Brown Brown Reflective Reflectance 30   32   30   32  30   22   17   15   30   8   9   8   9   Conductive (%) ParticlesContinuity Initial A A A A A A A A A A A A A Reliability After TCT A A AA A A A A A A A A A Insulation Initial A A A A A A A A A C C A AReliability After Aging A A A A A A A A A C C C A

As can be seen from Table 1, the anisotropic conductive adhesives usingthe light-reflective conductive particles of Examples 1 to 9 all had alight reflectance of 30% or more, and reflected blue light having awavelength of 450 nm without change. In addition, the continuityreliability and insulation reliability results were also good.

In contrast, since Comparative Examples 1 to 3 did not have alight-reflecting layer on the surface of the conductive particles, lightreflectance was about 10%. In Comparative Examples 1 and 2, shortcircuits occurred from the initial stage, and in Comparative Example 3,a short circuit occurred after aging, so that insulating reliability wasa problem. In Comparative Example 4, since silicon oxide was used forthe inorganic particles, the conductive particles had a brown color evenafter the inorganic particle layer was formed, and light reflectance wasabout 10%. The reason for this can be thought to be because thedifference between the refractive index of the silicon oxide and thebinder composition of the anisotropic conductive adhesive was less than0.02.

INDUSTRIAL APPLICABILITY

The light-reflective conductive particle of the present invention canprevent a deterioration in light-emitting efficiency and the occurrenceof a hue difference between the emission color of the light-emittingelement and the reflected color even if a light-reflecting layer thatcauses production costs to increase is not provided on a light-emittingdiode (LED) element, when producing a light-emitting device by flip-chipmounting a light-emitting element such as an LED element to a wiringboard using an anisotropic conductive adhesive. Therefore, theanisotropic conductive adhesive of the present invention is useful whenflip-chip mounting an LED element.

REFERENCE SIGNS LIST

-   -   1 core particle    -   2 light-reflective inorganic particle    -   3 light-reflecting layer    -   4 thermoplastic resin    -   10, 20 light-reflective conductive particle    -   11 cured product of thermosetting resin composition    -   21 substrate    -   22 connection terminal    -   23 LED element    -   24 n electrode    -   25 p electrode    -   26 bump    -   100 cured product of anisotropic conductive adhesive    -   200 light-emitting device

The invention claimed is:
 1. A light-reflective conductive particle foran anisotropic conductive adhesive used for anisotropic conductiveconnection of a light-emitting element to a wiring board, comprising acore particle coated with a metal material and a light-reflecting layerformed from light-reflective inorganic particles having a refractiveindex of 1.52 or more on a surface of the core particle, wherein thelight-reflecting layer contains a thermoplastic resin and thethermoplastic resin is a polyolefin.
 2. An anisotropic conductiveadhesive used for anisotropic conductive connection of a light-emittingelement to a wiring board, the adhesive comprising at-helight-reflective conductive particle comprising a core particle coatedwith a metal material and a light-reflecting layer formed fromlight-reflective inorganic particles having a refractive index of 1.52or more on a surface of the core particle, the light-reflective particlebeing dispersed in a thermosetting resin composition that forms a curedproduct having a light transmittance of 80% or more at a light pathlength of 1 cm to visible light having a wavelength of 380 to 750 nm. 3.The anisotropic conductive adhesive according to claim 2, wherein ablended amount of the light-reflective conductive particles based on 100parts by mass of the thermosetting resin composition is 1 to 100 partsby mass.
 4. The anisotropic conductive adhesive according to claim 2,wherein a reflectance of a 100 μm-thick cured product of the anisotropicconductive adhesive to light with a wavelength of 450 nm is at least15%.
 5. The anisotropic conductive adhesive according to claim 2,wherein a difference in the refractive index between the thermosettingresin composition and the light-reflective inorganic particles is 0.02or more.
 6. The anisotropic conductive adhesive according to claim 2,wherein the thermosetting resin composition includes an epoxy resin andan acid anhydride curing agent.
 7. A light-emitting device formed bymounting a light-emitting element by a flip-chip mounting method to awiring board with the light-reflective anisotropic conductive adhesiveaccording to claim 2 provided therebetween.
 8. The light-emitting deviceaccording to claim 7, wherein the light-emitting element is alight-emitting diode.